JPH10251382A - Coating composition based on polyepoxide hardener and polyacid hardener - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an improved coating composition suitable for a use as a top coat of an automobile. SOLUTION: This coating composition comprises a resin-like binder, an organic solvent and an arbitrary component found in a conventional topcoat composition of an automobile. The coating composition includes the resin-like binder having following components; (A) a polyepoxide; and (B) a polyacid hardener having <450 acid equivalent and having >3 carboxyl groups in average per molecule. The polyacid is formed by reacting (i) 1,2-acid anhydride of a cyclic dicarboxylic acid with (ii) a polyol component including an oligoester having <1,000 number average molecular weight and >3 hydroxyl groups per molecule in average.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to coating compositions suitable for use as automotive topcoats and, more particularly, to coating compositions suitable for use as transparent coats in colored-transparent composite coatings. About things.

[0002]

BACKGROUND OF THE INVENTION Colored-plus-transparent coating involves applying a colored or colored basecoat to a substrate, followed by applying the transparency of a transparent topcoat to the basecoat. . This coating is becoming more and more common as a unique finish on automobiles. This tinted-plus-clear coating has outstanding gloss and image discrimination, and transparent coats are particularly important for these properties. Two sets of clearcoat compositions, which are composed of polyols (eg, polyester polyols, polyurethane polyols and acrylic polyols) and polyisocyanate hardeners, are industry standard materials and Gives gloss and distinctiveness of the image. However, this polyisocyanate is difficult to handle, sensitive to moisture, and requires messy safety precautions.

It is an object of the present invention to provide the following colored-plus-clear coating system: this system avoids the problems of polyisocyanate hardeners, but has significant gloss and image discrimination. Provides a finish, so that this coating is useful as the first finish on an automobile.

[0004] US Patent No. 4,650,718 discloses a composite coloring method.
It discloses a coating composition suitable for use as a transparent coat in a transparent coating. The resinous binder of this coating composition is a polyepoxide hardener and a polyacid hardener. Polyacid curing agents that may be used include polymers containing carboxylic acid groups (eg, acrylic polymers, polyesters, polyurethanes), oligomers (eg, oligomers containing ester groups), and monomers. However, references include certain types of polyacid curing agents, such as those set forth in the claims of the present invention, which are useful in maintaining relatively high solids contents in coating compositions. , Found to provide excellent cure).

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coating composition suitable for use as a topcoat for automobiles, especially as a clearcoat in a composite color-plus-clear coating.

[0006]

The coating composition of the present invention comprises:
An improved coating composition suitable for use as an automotive topcoat, comprising a resinous binder, an organic solvent, and any components commonly found in automotive topcoat compositions. And the improvement is
In a resinous binder composed of: (A) a polyepoxide, and (B) a polyacid curing agent having an acid equivalent less than 450 and having an average of more than 3 carboxylic acid groups per molecule; The polyacid has the following (i)
And (ii) are formed by: (i) 1,2-anhydride of a cyclic dicarboxylic acid, (ii) having a number average molecular weight of no more than 1000, and averaging 3 per molecule A polyol component containing an oligomer ester having more than one hydroxyl group.

The method of the present invention is a method of applying a composite coating to a substrate, the method comprising applying a colored film-forming composition to the substrate to form a base coat;
And applying a transparent film-forming composition to the basecoat to form a transparent topcoat on the basecoat, wherein the transparent film-forming composition comprises the resinous binder. It is characterized by containing.

In accordance with the present invention, there is provided a coating composition comprising a resinous binder, an organic solvent, and any components commonly found in coating compositions. The resinous binder contains a polyepoxide curing agent and a polyacid curing agent. The polyacid hardener has an acid equivalent of less than 500 and has an average of more than 3 carboxylic acid groups per molecule. This polyacid curing agent has the following (i)
formed by reaction with (ii): (i) 1,2-anhydride of a cyclic dicarboxylic acid; (ii) having a number average molecular weight of no greater than 1000;
A polyol component containing an oligomer ester having an average of more than three hydroxyl groups per molecule.

The coating composition is particularly desirable for use as an automotive topcoat, especially as a clearcoat in a composite color-plus-clear coating.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The main components of the coating composition of the present invention are a polyepoxide hardener and a polyacid hardener.

Polyepoxides used in the practice of the present invention include aliphatic polyepoxides. Polyepoxides containing a cyclohexane oxide moiety are more preferred. The polyepoxides have low viscosity, high cyclic content, low molecular weight and high epoxy content.
These features in the formulation allow for the formation of high solids coating compositions with good cure response, as well as good physical and chemical properties in the resulting coating. A more preferred polyepoxide is a diepoxide, ie, an epoxide having 1,2-epoxy of the two epoxides.

A particularly preferred polyepoxide is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate. The diepoxides, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, and bis (3,4-epoxycyclohexylmethyl) adipate may also be used. These epoxides are ERL 4221, ERL 4289, and ERL 42, respectively.
99 available from Union Carbide.
Epoxides containing a cyclohexane moiety are also disclosed in U.S. Patent Nos. 2,890,194; 2,890,195; 2,890,196;
197; 2,890,210; 3,023,174 and 3,027,357.

In addition to polyepoxides based on cyclohexane moieties, low molecular weight epoxy condensation polymers, ie, polymers having an average 1,2-epoxy functionality of from 2 to 2.5 (the majority of the molecular moieties, ie, 50 Amounts greater than% by weight have two functionalities). Examples of such epoxy condensation polymers include polyglycidyl ethers of aliphatic and cycloaliphatic alcohols and polyglycidyl ethers of aliphatic and cycloaliphatic carboxylic acids. These polyepoxides can be formed by etherification or esterification of a cycloaliphatic alcohol or aliphatic alcohol or acid with an epihalohydrin (eg, epichlorohydrin) in the presence of an alkali. The product of etherification with a polyhydric phenol, which is then subsequently hydrogenated, can also be used. Examples of suitable alcohols and phenols are ethylene glycol; 1,2-propylene glycol; 1,2-cyclohexanedimethanol; 1,4-cyclohexanediol; and hydrogenated bisphenol A. Examples of suitable carboxylic acids include adipic acid and hexahydrophthalic acid.

The polyepoxides mentioned above have a relatively low molecular weight (generally not exceeding 1000 or less, preferably not exceeding 750, more preferably not exceeding 500) for the formulation of high solids coating compositions. ).

[0015] Alternatively, an acrylic polymer containing epoxy groups may also be included in the polyepoxide component. These polyepoxides increase the cure response of the resulting coating. Examples of suitable epoxy-containing acrylic polymers include ethylenically unsaturated monomers having at least one epoxy group (eg, glycidyl methacrylate and glycidyl acrylate) and at least one polymerizable ethylenically unsaturated monomer (eg, It has no epoxy groups; for example, copolymers with alkyl and methacrylic acids containing from 1 to 20 carbon atoms in the alkyl group. Examples of such monomers include methyl methacrylate, ethyl acrylate, butyl acrylate and butyl methacrylate. These polymers can be prepared by conventional free radical initiated organic solvent polymerization methods. These polymers are between 700 and 20,000, more preferably between 1000 and 10,000.
This molecular weight is determined by gel permeation chromatography using polystyrene standards.

Preferably, the polyepoxide is a mixture of a cyclohexane oxide moiety containing the polyepoxide and an epoxy-containing acrylic polymer. This mixture provides an optimal formulation of hardness, solids content and cure response.

The polyepoxide is usually present in the coating composition in an amount of about 20% to 75%, preferably 30% to 60% by weight, based on the total weight of the resin solids.
Exists. When an epoxy-containing acrylic polymer is used, the polyepoxide is based on 20% by weight of resin solids.
%, Preferably in an amount of 1% to 15% by weight.

The polyacid curing agent contains more than three carboxylic acid groups per molecule, which are reactive with the polyepoxide and form a crosslinked coating. Usually, this curing agent contains about 4 carboxylic acid groups per molecule. This acid functionality is achieved by opening the 1,2-anhydride of the cyclic dicarboxylic acid with the polyol component.
The carboxylic acid formed. Such high acid functionality (ie, acid groups per mole) is necessary in the resulting coating to obtain good cure response and to develop good physical and chemical properties. It is said. Furthermore, the high acid number allows the use of low viscosity polyepoxides. Thereby, a composition having low viscosity and high solid content having good fluidity and high gloss can be obtained.

The polyacid curing agent is preferably free of unsaturation (especially ethylenic unsaturation) and is free of chlorine substituents to obtain good external durability.

The polyol component contains an oligomer ester having an average of more than three hydroxyl groups per molecule. This component is preferably 20% by weight of the polyol component and the 1,2-anhydride of the cyclic dicarboxylic acid.
% To 70% by weight, more preferably 30% to 60% by weight
Used in the amount of Preferably, the oligomeric ester is formed by the reaction of a linear aliphatic dicarboxylic acid or a functionally equivalent material thereof with an aliphatic polyol having at least three hydroxyl groups. Along with this oligomer ester, to obtain the high hydroxyl functionality required to continuously form high acid functionality,
It is possible to tailor this polyol. During this time,
In order to obtain paint flexibility, a linear aliphatic group is introduced. Relatively low molecular weight oligomers allow for the formation of high solids coatings.

Among the linear aliphatic dicarboxylic acids that can be used are those containing at least 2 carbon atoms, preferably more than 2 carbon atoms, between the carboxyl groups. The dicarboxylic acids include, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dimeryl (dimer).
yl) acids (including mixtures of such acids). Preferably, the linear aliphatic dicarboxylic acid contains at least 6 carbon atoms. Adipic acid and sebacic acid are more preferred. In addition, materials equivalent to such dicarboxylic acids (eg, lower alkyl esters of dicarboxylic acids and anhydrides of dicarboxylic acids (here present as anhydrides)) can also be used.

The aliphatic polyol provides hydroxyl functionality in the ester oligomer. Some of the aliphatic polyols that can be used in practicing the present invention contain at least three hydroxy groups. Typically, these polyols contain from 3 to 12 carbon atoms. Particular examples include trimethylolpropane, ditrimethylolpropane, glycerol and pentaerythritol (including mixtures of such polyols). Diols such as ethylene glycol, propylene glycol and 1- (3-hydroxy-2,2-dimethylpropyl) -3-hydroxy-2,2-
A minor amount of dimethyl propionate (ESTER DIOL 204) (ie, not exceeding 50% by weight, based on the total weight of the organic polyol) may be included with the aliphatic polyol.

The oligomer ester is typically
It is prepared by reacting an excess mole of aliphatic polyol with a linear aliphatic dicarboxylic acid. During this time,
Water is removed during the condensation reaction and is allowed to react until completion of the reaction, which is evidenced by a low and substantially constant acid number. Typically, for each mole of linear aliphatic dicarboxylic acid, there will be at least 1.5 moles of aliphatic polyol. Preferably, for each mole of dicarboxylic acid, there are 2 moles or more of the polyol. Also, the reaction can be performed to the point where the reaction does not go to completion, such that the functionality of the unreacted acid is present. Such reaction products aid in curing.
However, unreacted diacid can crystallize during storage.

The ester-containing oligomers are typically of relatively low molecular weight, and do not exceed, on average, number average molecular weight, 1000, preferably 750.

In addition to the hydroxyl-containing ester oligomer, the polyol component may optionally also include additional polyols. Typically, these are low molecular weight organic polyols (eg, the polyols used in preparing the oligomeric esters) or, optionally, low molecular weight diols (eg, ethylene glycol, propylene glycol, butylene glycol, , 6-
Hexanediol and diethylene glycol). Also, polymeric polyols such as polyethylene glycol, polyoxytetramethylene glycol and poly (ethylene glycol adipate) may be included in the polyol component, and these optional polyols may improve the coating properties of the resulting coating composition. For example, the use of long chain glycols (eg, polyoxytetramethylene glycol)
Increase painting flexibility. In contrast, short-chain polyols (eg, trimethylolpropane) increase the hardness of this coating.

When these optional polyols are used, they are used in relatively small amounts (ie, not exceeding 50% by weight, based on the total weight of the polyol component).

[0027] The 1,2-anhydride of the cyclic dicarboxylic acid, which is subjected to the reaction with the polyol component, provides acid functionality in the polyacid curing agent. Preferably, the anhydride is present in an amount of from 20% to 80%, more preferably from 30% to 70% by weight, based on the total weight of the polyol component and the 1,2-anhydride of the cyclic dicarboxylic acid. Used. The 1,2-anhydride of the cyclic dicarboxylic acid that is subjected to the reaction with the polyol component provides an acid group that is highly reactive with the epoxy functionality, and provides excellent cure response in the resulting coating. provide. In addition, the annulus is provided to provide hardness and durability to the coating. This portion typically contains from 8 to 12 carbon atoms. Preferably, this annular portion is
Cycloaliphatic in order to obtain good external durability. Examples of suitable anhydrides include hexahydrophthalic anhydride and alkyl derivatives of hexahydrophthalic anhydride (eg, methyl hexahydrophthalic anhydride). Mixtures of hexahydrophthalic acid and methylhexahydrophthalic acid can also be used.

Alternatively, the acrylic dicarboxylic acid 1,2-
Lesser amounts of anhydride (ie, not more than 50% by weight, preferably not more than 30% by weight) can be used. These materials help to make the coating flexible.
Examples of such anhydrides include succinic anhydride, glutaric anhydride, and dodecenyl succinic anhydride.

The 1,2-anhydride and the polyol component of the cyclic dicarboxylic acid are usually brought together at the reaction temperature by slowly adding one component to the other. Preferably, the reaction is an inert gas (eg, nitrogen)
And in the presence of an organic solvent to dissolve the components and / or reduce the viscosity of the reaction mixture. Examples of suitable solvents include ketones (eg, methyl amyl ketone, diisobutyl ketone and methyl isobutyl ketone); aromatic hydrocarbons (eg, toluene and xylene). The reaction temperature usually does not exceed 150 ° C, preferably does not exceed 135 ° C, usually is in the range 70 to 135 ° C, preferably 90 to 12 ° C.
0 ° C. Catalysts such as amine catalysts are optionally
It can be used for this reaction. This reaction time can be varied to some extent mainly depending on the reaction temperature, the presence or absence of the catalyst, and the type of catalyst. Usually, the reaction is carried out until IR analysis indicates that all anhydride functionality has been consumed. However, it should be appreciated that the reaction can be carried out with an excess of anhydride such that free anhydride is present in the reaction mixture. Free anhydrides can actually improve coating properties, but are undesirable in terms of toxicity.

The equivalent ratio of anhydride to hydroxy groups of the polyol component is preferably at least 0.8: 1 (this anhydride is considered monofunctional) to obtain maximum conversion to the desired reaction product. It is. Ratios below 0.8: 1 can be used, but such ratios produce less favorable reaction products.

The polyacid curing agent of the present invention has a relatively low molecular weight. More specifically, the equivalent weight of this acid group is relatively low. Preferably, the equivalent weight of this acid group does not exceed 450, more preferably does not exceed 400, and most preferably does not exceed 350. Such low acid group equivalents allow for the formation of high resin solids compositions in combination with relatively high acid group functionality. This composition has excellent curing response,
And high crosslink density.

The polyacid curing agent is usually present in the coating composition in an amount of about 25% to 75%, preferably 35% to 65% by weight, based on the total weight of the resin solids. Exists inside.

In the composition of the present invention, the equivalent ratio of the carboxylic acid group to the epoxy group is as follows:
It is adjusted so that it will be about 1.2 equivalents to 0.8 equivalents, preferably 1.1 equivalents to 0.9 equivalents. This ratio is then sufficient to form a cured or crosslinked composition, as evidenced by the composition's resistance to organic solvents.

The polyepoxide-polyacid composition of the present invention is a liquid composition. The composition is preferably formulated into a liquid, high solids coating composition. That is, the coating composition contains more than 40% by weight of resin solids, preferably more than 50% by weight of resin solids. The solids content is determined by applying the coating composition at 76 ° F (24 ° C) to 25%.
Determined by formulating to have a No. 4 Ford Cup viscosity of 3030 seconds and determining this solids content according to ASTM 515/85.

[0035] In addition to the resinous component, the other component of the coating composition is an organic solvent. Typically used organic solvents are those used in preparing the polyacid curing agents. The solvents include ketones (eg, methyl isobutyl ketone and methyl amyl ketone) as well as aromatic hydrocarbons (eg, xylene and toluene).

The composition of the present invention also preferably contains a catalyst for accelerating the curing of epoxy groups and acid groups. Examples of suitable catalysts include basic substances. The catalyst includes organic amines and quaternary ammonium compounds such as N, N-dimethyldodecylamine, pyridine, piperidine, dimethylaniline, diethylenetriamine and tetramethylammonium acetate. When a catalyst is used, the amount of catalyst is typically from 0.1% to 8% by weight, based on the weight of the resin solids, preferably
It is 2% by weight to 5% by weight.

The following optional ingredients are also, if desired,
Can be used: this component includes, for example, auxiliary hardeners (eg, aminoplasts, plasticizers, antioxidants, UV light stabilizers), flow control agents, surfactants, and other formulation additives There is. Such materials are optional and typically comprise a total of about 20% by weight, based on the weight of resin solids.
Present in quantities up to.

The resin components described above can be formulated into clear coating compositions. Or, optionally, these components
It can be formulated with pigments to form paints. The pigment can be any of the conventional types of pigments, including: for example, iron oxide, lead oxide, strontium chromate, carbon black, carbon dust, titanium dioxide, talc, barium sulfate only. Rather, there are color pigments (eg, cadmium yellow, cadmium red, chrome yellow) and metal pigments (eg, aluminum foil, and mica coated with metal oxide).

The pigment content of this paint is usually
Expressed as resin weight ratio. In the practice of the present invention, when the film-forming coating composition of the present invention contains a pigment,
This pigment-to-resin weight ratio can be as high as 2: 1 and ranges for most colored coatings from 0.05 to 1: 1.

The coating composition of the present invention can be prepared by a conventional coating method (for example, brushing, spraying, dipping or flowing).
Can be applied to the substrate. However, the spray method gives the best appearance and is therefore more preferred. Any of the known spray methods can be used, for example, compressed air spray, airless spray, electrostatic spray, and either manual or automatic methods.

After applying the coating composition to the substrate, the painted substrate is heated to cure the coating. This curing operation drives off the solvent and activates the epoxy-acid crosslinking mechanism. This heating or curing operation
It is usually performed at a temperature in the range of 160-350 ° F (71-177 ° C). However, higher or lower temperatures can be used if necessary. The thickness of this coating is
Usually it is about 1-5 mils, preferably 1.2-3 mils.

Preferably, the compositions of the present invention are used to formulate a clear coating for use in a colored-plus-clear composite coating. With the application to coloring-plus-transparent coating, composite coating is applied to the substrate. The method includes applying a colored or pigmented film-forming composition to a substrate to form a basecoat, and applying a second film-forming composition to the basecoat to form a basecoat on the basecoat. Forming a transparent topcoat is included. The film-forming composition of this base coat is used for coatings, especially for automobiles (here,
Colored-plus-clear coatings have been found to be their optimal use) and can be any of the useful compositions. The film-forming composition usually comprises a resinous binder,
And a pigment that acts as a colorant. Particularly useful resinous binders are acrylic polymers, polyesters, including alkyds and polyurethanes. The resinous binder for the basecoat can be an organic solvent-based material. This substance
For example, U.S. Patent No. 4,220,679 (column 2, line 24 to column 4,
The substance described in line 40). Resinous binders as described in U.S. Pat. No. 4,540,766 may also be used. No. 4,403,003 and U.S. Pat.
Water-based coating compositions such as those described in US Pat. No. 7,679 may also be used as a binder in the basecoat composition. The resinous binder for this base coat can also be a polyepoxide-polyacid composition of the present invention.

The basecoat composition also contains a pigment, including a metallic colorant to obtain color. Examples of suitable pigments for this basecoat are described in US Pat.
20,679; 4,540,766; 4,403,003 and 4,147,67
Described in Issue 9.

The optional components in the basecoat composition are those known in the art for formulating surface coatings. This component includes surfactants, flow control agents, thixotropic agents, fillers, gasification inhibitors, organic co-solvents, catalysts, and other customary auxiliaries. Examples of these materials and appropriate amounts are described in US Patent No. 4,220,679 above;
Nos. 4,540,766; 4,403,003 and 4,147,679. Conventional spray methods and equipment, either for air spray or electrostatic spray, and for either manual or automatic methods, can be used. However, they are most often applied by spraying.

During the application of this base coat to the substrate,
The basecoat film is typically applied to the substrate at a thickness of about 0.1 mil to 5 mil, preferably about 0.1 mil to 2 mil. After the basecoat film is formed on the substrate, the solvent (ie, organic solvent and / or water) is driven out of the basecoat film by heating or simply air drying before applying the clear coat. Preferably, the heating step is performed so that, if necessary, the transparent topcoat composition does not pre-dissolve the basecoat composition (ie, striking in).
It is sufficient and only for a short time to ensure that it can be applied to the basecoat. Suitable drying conditions will depend on the particular basecoat composition and on the humidity at room temperature of certain water-based compositions. However, in general, drying times of about 1 to 5 minutes, and about 80 ° F to 175 °
A temperature of F (20 ° C to 79 ° C) is sufficient to ensure that mixing of the two coats is minimized. At the same time, the basecoat film must be sufficiently wetted by the transparent topcoat composition to obtain sufficient internal coat tack. Also, one or more basecoat applications and one or more topcoat applications can be applied to obtain an optimal appearance. Usually, while applying one coat, the previously applied base coat or top coat is flushed. That is, they are exposed to normal conditions for about 1 to 20 minutes.

The transparent topcoat composition is applied to the basecoat by any of the conventional coating methods described above. However, the spray method is more preferred. As noted above, the clear topcoat is preferably applied to the basecoat by a wet-on-wet method before the basecoat cures. The two coatings are then heated to cure both coating layers together. Curing conditions as described above can be used.

[0047]

The present invention is further defined by reference to the following examples. Unless otherwise indicated, all parts are by weight.

Example 1 An oligomeric ester containing 4 hydroxyl groups per molecule was prepared by reacting trimethylolpropane and adipic acid in a 2: 1 molar ratio as follows:

[0049]

[Table 1]

A reaction vessel equipped with a stirrer, a Dean-Stark trap, a cooler and a nitrogen purge is charged with trimethylolpropane and triphenyl phosphite, and the trimethylolpropane is melted under a nitrogen atmosphere. , Heated. Adipic acid was charged while the trimethylolpropane was melting. The reaction vessel was then heated to 190 ° C. while removing water with a Dean-Stark trap. The reaction mixture was heated at reflux with toluene (which was slowly added to the reaction mixture) and maintained at a reflux temperature of 190 ° C or less. The reaction was continued until an acid number of 10.5 was obtained.
Ester oligomer prepared as described above (6326
G) was diluted with 656 grams of toluene to give a solids content (measured at 110 ° C.) of 82.3 (theoretical = 90), an acid number of 8.2 and a hydroxyl number of 536.2.

The ester oligomer prepared as described above was reacted with methylhexahydrophthalic anhydride to form a polyacid hardener as follows:

[0052]

[Table 2]

^{1 The} methylhexahydrophthalic anhydride used in these examples was obtained as MILLDRIDE MHHPA from Milliken Chemical Company. This was shown as a 70/30 mixture of methyl hexahydrophthalic anhydride and hexahydrophthalic anhydride.

In a reaction vessel equipped with a stirrer, addition funnel, Dean-Stark trap, condenser and nitrogen purge,
The ester oligomer and toluene were charged and heated to reflux under a nitrogen atmosphere to remove residual water with a Dean-Stark trap. The components in the reaction vessel were then heated to 112 ° C and methylhexahydrophthalic anhydride was added through a dropping funnel to about 1.
Added over 5 hours. The reaction mixture was kept at 115-120 ° C. until infrared analysis indicated that all anhydride functionality had been consumed. The reaction mixture was then cooled to 107 ° C. and subsequently diluted with methyl isobutyl ketone. The resulting reaction product had a solids content of 72.3 (measured at 110 ° C), and 153.7
It had an acid value of The polyacid hardener described above (acid equivalent = 264 at 100% solids) is formulated into a clear coating composition as follows:

[0055]

[Table 3]

¹ Substituted benzotriazole UV light stabilizer obtained from Ciba-Geigy ² Bis (1,2,2,6,6,-, obtained from Ciba-Geigy
Pentamethyl-4-piperidinyl) decandioate ³ Polybutyl acrylate having a Mw value of about 10,000 and a Mn value of about 2400; 58.8% in xylene
At a solids content of ⁴ N, N-dimethyldodecylamine catalyst obtained from Akzo Chemical Co. ^{5 An} acrylic containing 40% glycidyl methacrylate, 20% methyl methacrylate, 20% butyl acrylate, and 20% butyl methacrylate Polymer; weight percent is
Based on the total weight of the monomers. This polymer has a Mn of 1456, determined by gel permeation chromatography using polystyrene standards, and
It has a solids content of 60% by weight. ⁶ Bis (3,4-epoxycyclohexylmethyl) adipate obtained from Union Carbide.

The components described above were mixed together in the order shown, with low shear agitation, to form a base mixture.

This base mixture was compounded with the polyacid curing agent described above as follows:

[0059]

[Table 4]

The components were mixed together in the order shown while mixing with low shear to form a coating composition. This composition has a No. 4 Ford cup viscosity of 26.7, and a 58
% Solids content.

Basecoat Composition A silver metal basecoat composition was prepared by mixing together polyester polyol, polyurethane polyol, aluminum foil, and other coating ingredients as follows:

[0062]

[Table 5]

¹ Polymer microparticles prepared according to Example 2 of US Pat. No. 4,147,688 and diluted with 2-hexoxyethanol on a 1: 1 volume basis. Polyester polyol prepared as described generally in Example A of U.S. Patent No. 4,410,688, except that xylene was used in place of ^2- methyl amyl ketone.
The polyester had an actual solids content of 78%, an acid number of 7.93, and a hydroxyl number of 271.23. ³ Polyurethane polyol prepared as described generally in Example 1 of U.S. Patent No. 4,540,766. This polyurethane polyol has an actual solids content of 77.6%, 5.52%
And a hydroxyl number of 80.73. ⁴ Monsanto from available aminoplast resins. ⁵ Pigment paste prepared by mixing together the following components:

[0064]

[Table 6]

⁶ Hydrogenated diglycidyl ether of bisphenol A (epoxy equivalent = 240) reacted with ⁶ phosphoric acid (1 molar equivalent of epoxy per equivalent of epoxy).

While stirring this component with a low shear force,
They were mixed together in the order shown to form a basecoat composition. This composition had a No. 4 Ford cup viscosity of 21.7 seconds and had a solids content of 54.9%.

The coating composition as described above was applied as a clear coat in a wet-on-wet application as follows: a silver metal base coat was spray applied to the prepared steel sheet, and Flashing at room temperature for 5-10 minutes resulted in the formation of a basecoat approximately 0.6 mil thick. The clear coat composition described above was sprayed onto the basecoat. This composite coating is then applied at 265 °
Cured at F (129 ° C) for 30 minutes. This transparent coat is about
It had a thickness of 1.6 mils. The composite coating was then measured for its gloss, image discrimination, hardness, wet resistance, and xylene resistance. The results are reported in Table 12 below.

Example 2 A polyacid curing agent similar to that used in Example 1 was prepared, except that hexahydrophthalic anhydride was used instead of MILLDRIDE MHHPA. This polyacid curing agent was formulated into a coating composition containing a polyepoxide. This coating composition was applied as a transparent coat in a colored-transparent formulation, and the properties of the composite coating were evaluated.

An ester oligomer was prepared as described in Example 1. This ester was then reacted with hexahydrophthalic anhydride to form a polyacid hardener as follows:

[0070]

[Table 7]

A reaction vessel equipped with a stirrer, Dean-Stark trap, condenser, addition funnel, and nitrogen purge was charged with the ester oligomer and a first portion of toluene. This component was heated to reflux under a nitrogen atmosphere and any water present was removed by a Dean-Stark trap. Then, at 102 ° C, the AR
MEEN DM-12D was added. At a temperature of 110 ° C., a first portion of hexahydrophthalic anhydride and methyl isobutyl ketone was premixed and added slowly to the reaction mixture. A second portion of the premixed hexahydrophthalic anhydride and methyl isobutyl ketone was added slowly to the reaction mixture at 110 ° C. The reaction mixture was then heated to 122 ° C. for 30 minutes and cooled to 110 ° C. and maintained at this temperature. The reaction mixture was maintained at about 110 ° C. until IR analysis indicated that all anhydride functionality had been consumed. The reaction mixture was then diluted to a 68% resin solids solution by adding the remaining portion of toluene and methyl isobutyl ketone. The obtained polyacid curing agent was treated with Gardner for 53 seconds.
It had a Gardner-Holdt viscosity, and an acid number of 152. This polyacid curing agent (acid equivalent = 251, 100% resin solids) was formulated into a coating composition as follows:

[0072]

[Table 8]

While stirring this component with a low shear force,
Mixing was performed in the order shown to form an additive mixture. The polyacid curing agent was then added to the additive as follows:

[0074]

[Table 9]

This component is stirred with a low shear force,
Mixing was performed in the order shown to form a coating composition. This composition has a resin solids content of 57.5% and an N of 26.2 seconds.
o.4 had a Ford cup viscosity.

Next, this coating composition was applied as a transparent coat by a colored-transparent composite coating. In forming this composite coating, a silver metal basecoat composition as described in Example 1 was first spray applied to the prepared steel sheet to a thickness of about 0.6 mil. This coating is at room temperature
A flash of 10-15 minutes was followed by a spray of clear coat composition. This composite coating is then
Cured at 121 ° C. for 30 minutes. The dry film thickness of this clear coating was about 2.2 mils. The properties of this coating are reported in Table 12 below.

Example 3 Except that the polyacid curing agent was post-reacted with glycidol and additional methylhexahydrophthalic anhydride to increase the acid functionality of the resulting polyacid curing agent. A polyacid curing agent similar to one was prepared. This polyacid curing agent was prepared as follows:

[0078]

[Table 10]

A reaction vessel equipped with a stirrer, addition funnel, condenser and nitrogen purge was charged with the polyacid curing agent of Example 1 and heated to 115 ° C. The glycidol addition was then started, and after approximately 25% addition, the o-sulfobenzoic anhydride catalyst was added. The reaction temperature was then maintained at a gentle reflux while continuing to add glycidol. The reaction mixture was then maintained at about 120 ° C until substantially all of the epoxy functionality had been provided for the reaction.

The reaction product prepared as described above
843.7 g of methylhexahydrophthalic anhydride
0.9 g was added slowly. During this time, the reaction temperature was raised to about 1
Maintained at 10-112 ° C. When all the methylhexahydrophthalic anhydride had been added, 7.7 g of ARMEEN DM-12D was added, and then the reaction temperature was raised to 120 ° C until IR analysis indicated that all the anhydride had been subjected to the reaction. C. was maintained. Next, 93.8 g of a mixture of methyl isobutyl ketone and toluene (69/31 by weight) was added to the reaction mixture.
To dilute to 70% solids.

This polyacid curing agent (acid equivalent = 283.5,100
% Solids) and then Example 2 as follows:
The formulation was generally formulated as described herein.

[0082]

[Table 11]

The components are mixed together while mixing with low shear to form a coating composition. This coating composition had a solids content of 55.8% and a No. 4 Ford cup viscosity of 26.5 seconds. When the coating composition is applied as a transparent to a colored-transparent composite coating as described in Example 2, the composite coating is applied as shown in Table 12 below.
Had the properties reported in.

[0084]

[Table 12]

¹ Measured on a 20 degree gloss meter manufactured by Gardner Instruments. ² C-Box Determined by C-Box manufactured by I2R,
Image discrimination (DOI). ³ Tukon hardness number determined by ASTM E-48. ⁴ Cross-hatch adhesion generally determined according to the method of ASTM D-3359. This tackiness is rated 0-5, with 5 indicating excellent tackiness. ^{5 Use the} painted substrate as the ceiling of the wet chamber,
Wet resistance was measured by directing the coating inside the chamber. Heat the chamber to 140 ° F (60 ° C) and place about 2 inches (3 cm) of water 3-5 inches below the painted panel (inclined panel). After exposure in the wet chamber for about 18 hours, the tack and gloss of the coating were measured and compared to the initial tack and gloss values before the wet test. ⁶ A series of standard pencils, varying from the hardest 6H to the softest 6B, were obtained, and the pencil hardness was determined by scratching the painted panel with the pencil of varying hardness until the paint was engraved. Xylene resistance was determined by placing a drop of ⁷ xylene on the paint for 3 minutes and then measuring the pencil hardness after wiping xylene spotting.

Example 4 Trimethylolpropane and 1- (3-hydroxy-2,2-
(Dimethylpropyl) -3-hydroxy-2,2-dimethylpropionate (ESTER DIOL 204, obtained from Union Carbide) was reacted with adipic acid to form a hydroxyl-containing ester oligomer, which was further
A polyacid curing agent similar to that used in Example 1 was prepared except that it was reacted with methylhexahydrophthalic anhydride to form a polyacid curing agent. This polyacid curing agent was then formulated into a coating composition along with the diglycidyl ether of hydrogenated bisphenol A. This coating composition was applied as a transparent coat on a steel plate. The properties of the cured coating were evaluated.

This oligomer ester was prepared as follows:

[0088]

[Table 13]

A reaction vessel equipped with a stirrer, a Dean-Stark trap, a condenser and a nitrogen purge was charged with trimethylolpropane, adipic acid, ESTER DIOL 204, triphenyl phosphite and 10 g of toluene. And heated to the distillation temperature to drive off the water. When the temperature of the reaction mixture reached 190 ° C, the remainder of the toluene was slowly added dropwise to the reaction mixture to maintain the distillation temperature below 190 ° C. The reaction was maintained at a temperature of about 186 ° C. until an acid number of 4.72 was obtained. Then the reaction mixture was cooled to room temperature. The acid value of the final reaction product was 4.14. This product has a Gardner
It had a Holt viscosity, a solids content of 80.6 (theoretical solids content = 90%) (measured at 110 ° C.), a hydroxyl number of 534, and an acid number of 4.3.

The ester oligomer prepared as described above was subjected to a reaction with methylhexahydrophthalic anhydride to form a polyacid curing agent as follows:

[0091]

[Table 14]

A reaction vessel equipped with a stirrer, addition funnel, Dean-Stark trap, condenser, and nitrogen purge was charged with the ester oligomer and toluene and heated to 110 ° C. Methylhexahydrophthalic anhydride was added via dropping funnel over 40 minutes. IR
The reaction mixture was maintained at about 110 ° C. until analysis indicated that all anhydride functionality had been consumed. The reaction mixture was then diluted with methyl isobutyl ketone. The resulting reaction product had a theoretical solids content of 70%, an acid number of 133.3, and an acid equivalent of 294.6, which
(Measured at 100% solids). The polyacid curing agent described above was formulated into a coating composition as follows:

[0093]

[Table 15]

¹ Diglycidyl ether of hydrogenated bisphenol A obtained from ¹ Shell Chemical Company.

The components described above were mixed together in the order shown, with low shear mixing, to form a coating composition. This composition had a solids content of 65%.
This coating composition was applied as a clear coat on a steel plate primer. 280 ° F (138 ° C)
And cured for 30 minutes. The resulting cured coating was hard and shiny and resistant to both acetone and methyl ethyl ketone.

Example 5 A polyacid curing agent similar to that of Example 1 was prepared except that a mixture of sebacic acid and adipic acid was used instead of adipic acid. This polyacid curing agent was formulated into a coating composition containing the polyepoxide of Example 4. This coating composition was applied to a steel sheet as a transparent coat. The coating was cured and the properties of the cured coating were evaluated. This oligomer ester was prepared as follows:

[0097]

[Table 16]

A reaction vessel equipped with a stirrer, Dean-Stark trap, cooler, and nitrogen purge was charged with trimethylolpropane, adipic acid, sebacic acid, triphenyl phosphite, and 10 g of toluene, and placed under a nitrogen atmosphere. At, heating was performed to the distillation temperature to drive off water. When the reaction temperature reached 190 ° C, toluene was slowly added dropwise to keep the distillation temperature below 190 ° C. About 312
The reaction is allowed to run at 198 ° C until milliliters of water are removed.
Maintained. This temperature was then maintained between 160 and 170 ° C. until an acid number of 11.6 was obtained. The reaction mixture was then diluted with the remaining toluene to a theoretical solids content of 90%.

The ester oligomer had an actual solids content of 88.0%, a hydroxyl number of 560.5, a Gardner-Halt viscosity of 72 seconds, and an acid number of 10.5.

The ester oligomer described above was subjected to a reaction with methylhexahydrophthalic anhydride to form a polyacid hardener as follows: The ester-containing oligomer prepared as described above, methyl A mixture of isobutyl ketone and ARMEEN DM-12D was prepared as follows:

[0101]

[Table 17]

Mixture 1 prepared as described immediately above
3.5 g were mixed with 16.2 g of methylhexahydrophthalic anhydride and stirred at 240 ° F (116 ° C) until IR analysis indicated that all anhydride functionality had been consumed.
Heated for hours. The resulting reaction product had a solids content of 76.2%. The product was diluted with additional methyl isobutyl ketone to a 70% solids solution. This polyacid curing agent was formulated into a coating composition as follows:

[0103]

[Table 18]

While mixing this component with a low shear force,
They were mixed together in the order shown to form a coating composition. This composition had a solids content of 65%. This was poured on a steel plate and cured at 280 ° F (138 ° C) for 30 minutes to obtain a hard, glossy and flexible film resistant to methyl ethyl ketone.

Example 6 A polyacid curing agent similar to that of Example 1 was prepared, except that di-trimethylolpropane was used instead of tolmethylolpropane. This polyacid curing agent is combined with hydrogenated bisphenol A diglycidyl ether
Formulated in a paint composition. This coating composition was applied as a transparent coat on a steel plate. The cured coating and the properties of the cured coating were evaluated. This ester oligomer was prepared as follows:

[0106]

[Table 19]

A reaction vessel equipped with a stirrer, Dean-Stark trap, condenser and nitrogen purge is charged with trimethylolpropane, adipic acid and triphenyl phosphite and heated to the distillation temperature under a nitrogen atmosphere. To remove the water. When the reaction temperature reached 190 ° C, toluene was slowly added to the reaction mixture to keep the distillation temperature below 190 ° C. The reaction mixture was maintained until an acid number of 6.5 was obtained. The reaction mixture was then diluted with methyl isobutyl ketone to a theoretical solids content of 75%. The resin was clear and colorless. The resin had a Gardner-Halt viscosity of 16.5 seconds.

The ether oligomer prepared as described above was reacted with methylhexahydrophthalic anhydride to form a polyacid hardener as follows:

[0109]

[Table 20]

The above ingredients were mixed together, placed in a 1 quart jar, and placed in an oven at 240 ° F. (116 ° C.) for 7 hours. IR analysis indicated that the reaction mixture still contained some anhydride functionality. The jar was left at room temperature for 5 days. Thereafter, IR analysis indicated that all the anhydride functionality had been consumed. The reaction mixture had a solids content of 74.8 (measured at 110 ° C.), an acid number of 161.8, and a hydroxyl number of 48. The polyacid curing agent described above (acid equivalent = 259.3, 100% solids) was formulated into the coating composition as follows:

[0111]

[Table 21]

While mixing this component with a low shear force,
They were mixed together in the order shown to form a coating composition. This composition had a solids content of 65%. When the coating composition was cast on a steel sheet and cured at 280 ° F (138 ° C) for 30 minutes, a glossy, hard and very flexible coating was obtained. This coating was resistant to methyl ethyl ketone.

Automotive topcoat, especially composite coloring
A coating composition suitable for use as a clear coat in a plus-clear coating is disclosed. The resinous binder in the coating composition was composed of polyepoxide and 3 per molecule.
A polyacid curing agent having more than one carboxylic acid group. The polyacid curing agent is formed by reacting a polyol component containing an oligomer ester having an average of more than three hydroxyl groups per molecule with a 1,2-acid anhydride of a cyclic dicarboxylic acid. The polyacid curing agent can be a very effective curing agent for high solids coating compositions due to its relatively high acid functionality, low molecular weight and better reactivity.

[0114]

According to the present invention, there is provided a coating composition suitable for use as a topcoat for automobiles, especially as a clearcoat in a composite color-plus-clear coating. The present invention avoids the problems of polyisocyanate hardeners, but provides a finish with significant gloss and image discrimination, so that the coating is useful as the first finish in an automobile. The polyacid curing agent used in the present invention has a relatively high acid functionality, has a low molecular weight and exhibits good reactivity, so it is a very effective curing agent for high solids coating compositions. obtain.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Edward Lee Dufford United States Pennsylvania 16055 Server, server load 837 (72) Inventor Joseph Andrew Cronica United States Pennsylvania 16055 Server, Orchard Drive 105

Claims (2)

[Claims] 1. An improved coating composition suitable for use as an automotive topcoat, the coating composition comprising a resinous binder, an organic solvent, and a composition commonly used in automotive topcoat compositions. Containing optional components found, the improvement resides in a resinous binder containing the following components: (A) polyepoxide, and (B) having an acid equivalent less than 450, and averaging three per molecule. A polyacid curing agent having more than one carboxylic acid group;
formed by reaction with (ii): (i) 1,2-anhydride of a cyclic dicarboxylic acid, (ii) having a number average molecular weight not greater than 1000, and averaging three per molecule. A polyol component containing an oligomer ester having an excess of hydroxyl groups. 2. A method of applying a composite coating to a substrate, comprising applying a colored film-forming composition to the substrate to form a basecoat, and applying a transparent film-forming composition to the basecoat. A method comprising forming a transparent topcoat on a basecoat, wherein the transparent film-forming composition is characterized by containing a resinous binder comprising the following components: (A) a polyepoxide, and (B) A polyacid curing agent having an acid equivalent of less than 450 and having an average of more than 3 carboxylic acid groups per molecule;
And (ii) formed by the reaction of: (i) 1,2-anhydride of a cyclic dicarboxylic acid, (ii) having a number average molecular weight of not more than 1000, and averaging three per molecule A polyol component containing an oligomer ester having more than one hydroxyl group.